Environmental concerns are becoming increasingly more prevalent and are having more pronounced effect on many industries which generate wastes which have environmental impact. One such industry is the United States pulp and paper industry which generates effluents which present environmental concerns. Future water pollution and other environmental regulations may require this industry to reduce substantially the color and other constituents in its effluents. While the effluents from most pulp or paper-making operations contain lignin or its degradation products, the effluents from the first alkaline extraction stage in the chlorine bleach plant are of special concern because they are the major source of color and other undesirable constituents in pulp and paper-making effluents. The main contributors to such undesirable constituents in bleach plant effluents are polymeric, chlorinated, heavily oxidized degradation fragments of lignin.
Certain proposals have been advanced for reducing the effluent volume through recycling and for color removal, but such proposals have not been accepted as solutions to the problem. Such bleach plant effluents are not easily recycled because of the potential corrosion problems created by their high chlorine content. Further, color removal by either oxygen bleaching or dynamic bleaching and some tertiary color removal processes, such as ultrafiltration, carbon adsorption and lime precipitation, have been investigated, but implementation of these processes would be prohibitively expensive and therefore have not been adopted.
There have been attempts at using various biological processes to decolorize effluents. These processes have met with varying success, but none have proven practical for industrial or commercial use. One study has shown that various isolated fungi can remove up to 80% of the color from kraft pulp mill effluents, in batch reactions. Nova Scotia Research Foundation, Environment Canada, Cooperative Pollution Abatement Research Project Report No. 208-1 (1974). However, when this process was scaled up and run on a continuous basis to stimulate industrial conditions, only 50% decolorization was achieved. An attempt has also been made to use algae to decolorize kraft bleach plant effluents. British Columbia Research, Environment Canada, Cooperative Pollution Abatement Research Project Report No. 410-1 (1976). The algae method only removes 70% of the color after 20 days. This time lag prohibits use of the process by industry. Another group has attempted to use white-rot fungi to decolorize effluents. Fukuzumi, Nishida, Aoshima, and Minami, Decolorization of Kraft Waste Liquor with White-Rot Fungi (pt. 1), 23 (6) Journal of the Japan Wood Research Society 290 (1977). Although the process removes up to 90% of the color, it requires an extremely complex growth medium containing glucose or ethanol, asparagine, and aspartic acid, among other things. No attempt was made to recycle the fungal biomass, or to use spent mycelium as a secondary source of carbon and nitrogen for the fungi. No recognition was made that nutritional conditions must be different for separate stages of fungal growth and decolorization of effluents. Also, the process was much too slow and the active lifetime of the fungus too short for adaptation to industrial or commercial use.
With the foregoing in mind, it is an object of the present invention to provide a low-cost, industrial or commercial process of treating effluent from a pulp or paper-making operation to improve the environmental character thereof.
A more specific object of the present invention is to provide a process of treating effluent with a white rot fungus to degrade lignin and its polymeric degradation products in which the rate of decolorization, total color units removed and active lifetime of the fungus are greatly increased.